The properties of fluorescent derivatives of o-phthaldiadehyde were studied in order to facilitate the use of this compound in the assay of amino acids and the labeling of proteins. The reaction rates and fluorescence parameters were measured and discussed in relation to other reagents and methods for amino acids. Various solvents commonly used in phosphorimetry were tested for inhibitory effects on alcohol dehydrogenase. Some alcohols were inhibitory, while some salts activated the enzyme, so that the interpretation of phosphorescence data should include the possibility of conformational change due to the matrix. An artifact has been found and characterized in the operation of the Los Alamos Flow Cytometer and cell sorter. When cell volume is being measured in this instrument, the fluorescence of the suprovitally stained cells decreased due to electrolysis. The mechanism of bleaching apparently involves generation of chlorine at the anode.